When the GMA welding arc becomes erratic, should the operator adjust the power source? Not necessarily. If the voltage and wire feed speed values currently used previously worked well, and if the correct shielding gas and flow rates have been selected, worn components are likely at the root of the problem.

Liners, tips and other gun components need routine inspection to ensure consistent GMAW performance. Good maintenance also prevents rework, eliminates unplanned downtime and maximizes gun life. The following maintenance practices apply to most brands of guns. Before working on a gun, review the operator’s manual and follow appropriate safety precautions to prevent burns or electric shock.

Cleaning Liners

Erratic GMA performance occurs when excessive friction causes the electrode stick or slip. When wire feed speed slows, yet voltage remains constant, the electrode will melt back from the weld puddle more quickly and produce an erratic arc. One of the most common culprits is a gun liner that has become clogged with wire shavings and other particulates.

Operators everywhere should get in the habit of blowing out the liner with compressed airwhen installing a new spool of wire. For GMAW systems with a high arc-on time, operators might consider blowing out the liner more frequently (experience will dictate the need).

Blow out liners when installing a new spool of wire.

How rapidly a liner clogs varies greatly. Over-tensioningthe drive rolls on flux cored electrodes can clog a liner quickly. Electrodes exposed to the elements, especially humidity and salt air, can quickly clog a liner, as can a poor quality electrode. Different electrodes manufacturers use different drawing compounds and substances to coat and finish the electrode. As a result, some clog liners faster than others — sometimes in half a spool or less. To keep liners cleaner longer, consider installing cleaning pads during the next scheduled maintenance. Use good cleaning pads and secure them properly, otherwise bits of the pad may end up clogging the liner.

Wire shavings and other debris build up inside the liner, creating drag that causes the wire to stick or slip when feeding.

For a clearer indication of particulate volume inside the gun liner, place a sheet of paper or cardboard under the gun to provide better contrast. If the arc is erratic and blowing out the liner reveals only small amounts of particulate, the liner is worn and should be replaced. For example, in the Tweco test lab, using a leading brand of 1/16-in. diameter ER70 S-6 electrode, applying these guidelines, we most frequently replace the liner after two 60-lb. spools.

Replacing Liners

To simplify liner stocking, companies running several models of guns can use a “universal conduit liner.” These two-piece liners feature a liner crimped with a threaded wire guide and adapters to make it compatible with most guns.

To replace a liner, remove the old liner, lay the new liner next to it on the floor and cut the new liner to the exact same length. A liner that is too short can interfere with feeding performance and lead to an erratic arc. Further, if a void exists between the liner and the diffuser, it could create a spot that traps the wire and leads to a bird nest.

When trimming the new liner, use sharp, premium quality side cutters. To produce a clean cut, place the cup side of cutters against the liner and orient the cutters so that they cut against the curl of the liner. Cutting with the curl tends to produce a burr on the inside edge of the liner, where it could drag against the wire.

Never use dull cutters or whelpers to trim a liner. Rather than cleanly cut through the tough piano wire used for liners, they will most likely deform the liner and/or spread out the coils. Never use a cutting disc (e.g.,RotoZip or similar tool), as it can leave a sharp edge that drags against the electrode and creates shavings. Should the cut liner have a burr, use a hand file to remove it. Otherwise, discard it and try again.

As with any mechanical system, don’t use excessive force in when installing a new liner. If the liner hangs up, twist it in a counter clockwise direction so as not to uncoil the liner. If the liner doesn’t fit, the liner could be too long (in which case, trim it) or it could be bent. If the liner is bent, discard it, as a bent liner can promote erratic feeding.

Some gun models use small screws to keep the liner from twisting. Do not remove or discard those screws. First, if the liner twists independently from the gun cable, it can increase or decrease the length of liner relative to the length of the gun cable. Second, an absent screw may permit shielding gas to escape through the hole instead of coming out the diffuser, which may lead to insufficient gas coverage or excessive gas flow to compensate for lost gas.

Spatter and Tips, Nozzles and Diffusers

The GMA process, especially short circuit transfer, inherently produces spatter. A percentage of operators inherently feel compelled knock spatter off by banging the gun on the welding table or work piece. Banging the gun doesn’t do much to remove spatter, but it’s a great way to loosen component connections at the front of the gun. Don’t bang the gun!

Anti-spatter compound can minimize the effects of spatter and extend consumables life.

Use whelpers, a nozzle reamer or an even an old pocketknife to remove spatter from the nozzle and contact tip. If spatter has adhered to the contact tip to the point where it can’t be easily removed, discard the tip rather than deform the orifice trying to remove spatter. Note that the spatter from a well-tuned arc is finer and easier to remove (and anti-spatter dip or spray will also help). Large spatter balls may indicate the need to further fine tune parameters, or perhaps your base metal has excessive mill scale or oil.

Spatter also finds its way into gas diffuser ports. Inspect the diffuser for spatter, remove the spatter or replace the diffuser if necessary. Caution: do not remove the nozzle and lay a live gun on the welding table. The gas diffuser is electrically hot. If the trigger is accidentally activated, electricity will take the path of least resistance through the diffuser causing damage. Also, note that the diffuser threads are prone to damage if a gun is left sitting around with the diffuser threads exposed.

Contact Tips

Contact tips should be replaced when the operator can observe wear in the ID. Drop-in style contact tips can be rotated 90 degrees to extend service life. Threaded contact tips should be wrench-tight to ensure good conductivity.

When welding at higher amperages and holding a tight arc, the electrode becomes preheated almost to the contact tip. There, the tip acts like a kiln; the electrode drawing compound, shavings and particulates fuse into a sludge. As sludge builds, the tip inside diameter (ID) narrows and eventually causes the electrode to bind, creating an erratic arc or even a burn back. In such situations, change the tip more frequently.

Note that the elemental composition and grain structure of a metal directly affects its electrical and thermal conductivity, as will a parts’ design and machining tolerances. As such, use premium quality contact tips to help ensure consistent GMA performance.

Insulator, Diffuser and Conductor Tube

As insulators repeatedly heat and cool over time, they can lose their volume and the connection between them and the gas diffuser and/or conductor tube becomes wobbly (and using the gun as a chipping hammer greatly exacerbates the problem).Worn insulators should be replaced, as loose connections may lead to gas leaks, poor conductivity or excessive electrical resistance, all of which will manifest themselves as arc instability or porosity.

Some diffusers and conductor tubes have O-rings, which should be inspected and replaced if worn. Inspect all threaded connections for wear or damage and replace if worn.

Gun Handle and Trigger

Periodically check the screws on gun handles to ensure that they remain tight.

These components can take an incredible amount of use and abuse and rarely need maintenance, other than checking to ensure the screws in the gun handle are secure. Triggers do sometimes become magnetized, attract metallic dust and cause contactors to close prematurely or the trigger to stick. In this case, replace the trigger.

There is a contingent of old-school welders who bend the contactors inside the trigger to reduce the distance the trigger travels before it engages the welder. They prefer this “hair trigger” to reduce hand fatigue. Gun manufacturers cannot endorse such unauthorized modifications. A better solution, and one which doesn’t involve altering the gun, would be to use a wire feeder with trigger hold control or a power source with 4T capabilities for GMAW.

Cables

Inspect the gun and work clamp cables daily to ensure that the cable jacket is free from cuts that could expose copper wiring and lead to electrical accidents. Replace — never tape or otherwise repair — any cut cable. Otherwise, the risk from shock is too high.

Never tape a cut cable, as that is insufficient protection against shock. Always replace damaged cables with new ones.

When done welding, don’t drape the gun over the edge of the welding table, power source or in a position where it places excessive stress on the area just past the gun handle. Inshops that get cold overnight, the once warm gun cable may have cooled in a kinked position that, at a minimum, can be a pain to use until it warms up again.

Also, while guns can weld with the cable tied into a knot, why place excessive stress on the system or risk binding the wire and or a bird’s nest? Keep the gun cable relatively straight when welding, and coil and hang it properly at the end of the day.

Feeder Connection

Periodically inspect the O-rings on the feeder connection; replace worn O-rings to prevent shielding gas leaks. Avoid dropping the back-end of the gun, as the “power pin” on some models is especially susceptible to deformations that hinder wire feed performance.

When re-connecting the gun to the wire feed system, push the gun all the way in and lock it in place with the set screw. Check this connection every week or so, as loose connections lead to a voltage drop that especially impacts advanced processes, such as modified/enhanced short circuit transfer and pulsed GMAW.

Gun maintenance procedures follow common sense guidelines to ensure consistent GMAW performance and maximum uptime. Maintaining components that cost just a few dollars and a couple of minutes to replace is a much better choice than grinding out a bad arc start or unplanned downtime in the middle of a shift.